Evolution of Earthworms

What are Earthworms?

An earthworm is an invertebrate living on soil. They present a tube-within-a-tube body system, are externally segmented with similar internal segmentation, and typically have setae on all sections. They can be seen globally where soil, temperature, and water allow.

Earthworms are commonly seen in soil, eating a wide diversity of organic matter. This organic matter covers plant matter, living fungi, bacteria, rotifers, protozoa, nematodes, etc. An earthworm’s digestive system runs the width of its long body. It breathes through its skin. It has a double transportation system made of coelomic fluid that flows within the fluid-filled coelom and an uncomplicated, circulatory system. It has a peripheral and central nervous system. Its central nervous system comprises of two ganglia over the mouth, one on either side, attached to a nerve floating along its length to sensory cells and motor neurons in each segment. Large numbers of chemoreceptors narrow near its mouth. Longitudinal and circumferential muscles edging each component let the worm move. Related sets of muscles outline the gut, and their efforts move digesting food toward the anus of the worm.

Evolution of the Earthworms

Research reveals that all living earthworms’ ancestors apparently lived over 220 million years ago, making earthworms about as old as dinosaurs and mammals. Historic records estimate the deviations between the Southern and Northern Hemisphere subgroups of the two principal branches of earthworms fall between 162-174 million years ago, coinciding with the supercontinent breakup Pangaea 180-200 million years ago and supporting the hypothesis that continental breakup affected early earthworm diversification. This also indicates that earthworms likely occupied Antarctica before the continent’s southward drift made it hostile to most earthly animal life.

Genetic Evolution of Earthworms

Earthworm populations in contaminated soils can stand high internal body loads of specific metal contaminants, like zinc and lead. In fact, they thrive in contamination levels that would ultimately kill off earthworms that are used to decontaminate soils.

Few scientists believe that earthworms evolved in response to this environmental stress in the surroundings.

Scientists have found that the two populations of earthworm- one native to the mine site and others’ living elsewhere show remarkable differences.
The earthworms who are native to the mine sites can hold more metals in their body and are also able to convert a higher portion into a non-toxic form of insoluble.

So, conclusively, scientists suggest that the genetic information divided earthworms into different groups- one living in mines can convert metals into non-toxic forms, and the other one unable to handle the toxins in soil because of historic ‘non-exposer’ to the metals.

The link between genes and earthworm’s ability to partition the metals is the evolutionary gift to these crawling species.

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